Post-processing apparatus and image forming system

ABSTRACT

A post-processing apparatus includes a post-processing unit performing post-processing for a sheet ejected from a former-stage apparatus, a post-processing time calculating unit calculating a time required for the post-processing based on a content of the post-processing, a time comparing unit comparing the time required for the post-processing and a sheet interval between sheets ejected from the former-stage apparatus, an overlapping conveying unit overlapping a plurality of sheets ejected from the former-stage apparatus and conveying the overlapping sheets on an upstream side of the post-processing unit, and a control unit controlling the overlapping conveying unit, wherein the control unit changes the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of sheets ejected from the former-stage apparatus where the time required for the post-processing is determined to exceed the sheet interval based on a comparison result of the time comparing unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a post-processing apparatus that performs post-processing for a sheet on which an image is transferred by an image forming apparatus and an image forming system that includes the image forming apparatus and the post-processing apparatus.

2. Description of the Related Art

In image forming apparatuses that form images and transfer the images to a sheet such as a copying machine, a printer, a facsimile, and a multifunction periphery, post-processing can be performed for the sheet to which images have been transferred as desired. Examples of the post-processing include stapling, saddle stitching, and punching. The post-processing is performed by a post-processing apparatus that is connected to the later stage side of an image forming apparatus. In addition, it is not necessary for the post-processing apparatus to be connected immediately next to the image forming apparatus.

In latest image forming apparatuses, implementation of high speed has progressed so as to improve the productivity, and a time interval for each sheet (hereinafter, referred to as a sheet interval) in which the sheet is conveyed is further shortened. On the other hand, in the post-processing, a processing time according to the details of the post-processing is necessary, and the implementation of high speed has not progressed as much as that of the image processing apparatus. As a result, when the time that is required for the post-processing is secured, as illustrated in FIG. 7( a) for a case where overlapping conveyance is not performed, it is necessary to secure a long sheet interval, and there occurs a problem of degrading the implementation of high speed of the apparatus.

Thus, a post-processing apparatus has been proposed which is configured not to decrease the productivity of an image forming apparatus by arranging an overlapping conveying unit that allows sheets to stay (pre-stock) in the post-processing apparatus and can convey a plurality of the sheets in an overlapping manner (for example, Patent Literature 1 and 2).

In Patent Literature 1, a post-processing time is secured by pre-stocking N sheets that are defined in advance.

In addition, in Patent Literature 2, in a system that includes a plurality of stages of post-processing apparatuses, a time that is necessary for post-processing of a later stage is acquired, and the timing for ejecting a sheet to the post-processing apparatus of the later stage is controlled in accordance with the time by a post-processing apparatus of the former stage that receives the sheet from an image forming apparatus.

When overlapping conveyance is performed, as illustrated in FIG. 7( b), in a case where a time that is required for the post-processing is longer than the sheet interval, by performing overlapping conveyance of sheets corresponding to a number set in advance therebetween, the post-processing can be performed without affecting the sheet interval. In the example of this apparatus, four sheets are conveyed in an overlapping manner. When a case where overlapping conveyance is not performed, but the sheet interval is lengthened and a case where the overlapping conveyance is performed are compared with each other, as illustrated in FIG. 7, at a time point at which a second page of the next bundle is conveyed in a case where the overlapping conveyance is not performed, the fifth page of the next bundle can be conveyed in a case where the overlapping conveyance is performed. It is known that the productivity can be maintained to be high by performing overlapping control.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-Open No.     2010-159131 -   Patent Literature 2: Japanese Patent Application Laid-Open No.     2010-18399

However, the number of sheets that are conveyed in an overlapping manner inside the post-processing apparatus increases in accordance with the implementation of high speed of the image forming apparatus. According to the above-described conventional technique, the number of overlapping sheets is determined based on sheet information (a sheet size and a post-processing mode) that is notified in advance, and accordingly, even in a case where the sheet interval becomes longer due to a factor of a further upstream side than the post-processing apparatus, the post-processing apparatus is maintained to wait at an overlapping position until the set number of overlapping sheets is reached.

However, as the number of overlapping sheets increases, the more the number of overlapping sheets is, the higher the possibility of alignment mismatching is. In addition, in a case where the number of overlapping sheets is large, there is concern that the performance of conveyance may deteriorate due to a change in the sheet status (curling or the like) that is caused by an environment condition, a sheet condition, and a printing condition.

On the other hand, in a case where the number of overlapping sheets is decreased, the implementation of high speed of the image forming apparatus is encumbered.

The invention is devised based on the above-described situations, and at least one of the object thereof is to provide a post-processing apparatus and an image forming system that can resolve problems such as alignment mismatching by decreasing the number of sheets conveyed by the post-processing apparatus in an overlapping manner as much as possible without hindering the implementation of high speed of the image forming apparatus.

SUMMARY OF THE INVENTION

To achieve at least one of abovementioned objects, a post-processing apparatus reflecting one aspect of the present invention comprises:

a post-processing unit that performs post-processing for a sheet ejected from a former-stage apparatus;

a post-processing time calculating unit that calculates a time required for the post-processing based on a content of the post-processing;

a time comparing unit that compares the time required for the post-processing and a sheet interval between sheets ejected from the former-stage apparatus with each other;

an overlapping conveying unit that overlaps a plurality of sheets ejected from the former-stage apparatus and conveys the overlapping sheets on an upstream side of the post-processing unit;

and a control unit that controls the overlapping conveying unit, in which the control unit changes the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of sheets ejected from the former-stage apparatus in a case where the time required for the post-processing is determined to exceed the sheet interval based on a comparison result of the time comparing unit.

In the above-described post-processing apparatus, it is preferred that the control unit changes the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of the sheets ejected from the former-stage apparatus at the time of maintaining same set in the plurality sets for printing in an image forming apparatus arranged on a former stage of the post-processing apparatus.

In addition, in the above-described post-processing apparatus, it is preferred that the control unit change the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of the sheets ejected from the former-stage apparatus at the time of occurring different set in the plurality sets for printing in an image forming apparatus arranged on a former stage of the post-processing apparatus.

In addition, in the above-described post-processing apparatus, it is preferred that the control unit perform control of ejecting the sheets overlapping each other in the overlapping conveying unit toward the post-processing unit in a case where the post-processing unit disposed on a downstream side of the overlapping conveying unit is in a state in which sheets can be received.

In addition, in the above-described post-processing apparatus, it is preferred that the control unit determines the state in which sheets can be received based on whether or not the post-processing for sheets sent to the post-processing unit in advance has been completed.

In addition, in the above-described post-processing apparatus, it is preferred that the control unit determines the state in which sheets can be received based on whether or not a predetermined time has elapsed after a final sheet is sent to the post-processing unit for the post-processing.

In addition, in the above-described post-processing apparatus, it is preferred that the former-stage apparatus be an image forming apparatus.

Furthermore, in the above-described post-processing apparatus, it is preferred that the former-stage apparatus includes a different type of a post-processing apparatus that has a post-processing unit other than the post-processing unit.

To achieve at least one of abovementioned objects, an image forming system reflecting one aspect of the present invention comprises:

an image forming apparatus to form an image and transfer the image to the sheet;

a post-processing apparatus being located on a later stage side of the image forming apparatus and including a post-processing unit to perform post-processing for a sheet ejected from a former-stage apparatus and an overlapping conveying unit to overlap a plurality of sheets ejected from the former-stage apparatus and convey the overlapping sheets on an upstream side of the post-processing unit;

a post-processing time calculating unit to calculate a time required for the post-processing based on a content of the post-processing;

a time comparing unit to compare the time required for the post-processing and a sheet interval between sheets ejected from the former-stage apparatus of the post-processing apparatus with each other; and

the control unit according to any one of the above-described post-processing apparatus.

In the above-described the image forming system, it is preferred that at least one of a different type of a post-processing apparatus having a post-processing unit other than the post-processing unit is connected in sequence to the former stage of the post-processing apparatus in a later stage side of the image forming apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view that illustrates the mechanical configuration of an image forming system that includes a post-processing apparatus according to an embodiment of the invention.

FIG. 2 is a diagram that illustrates an example of the operation of an overlapping conveying unit.

FIG. 3 is a control block diagram.

FIG. 4 is a diagram that illustrates overlapping and conveying control operations.

FIG. 5 is a diagram that illustrates another example of the overlapping and conveying control operation.

FIG. 6 is a flowchart that illustrates the sequence of the overlapping and conveying control operation,

FIG. is a diagram that illustrates conventional sheets conveying and overlapping.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the invention is described.

As illustrated in FIG. 1, an image forming system is configured by an image forming apparatus 1, a first post-processing apparatus 2 that is connected to a later stage of the image forming apparatus 1, and a second post-processing apparatus 3 that is connected to a later stage of the first post-processing apparatus 2. The second post-processing apparatus 3 corresponds to a post-processing apparatus according to an embodiment of the invention, and the above-described image forming system corresponds to an image forming system according to an embodiment of the invention.

A post-processing unit included in the post-processing apparatus performs predetermined post-processing for sheets ejected from the former stage, and the type of the post-processing is not particularly limited. Examples of the post-processing include stapling, saddle stitching, punching, and a binding process as illustrated FIG. 1. In addition, in the post-processing apparatuses, post-processing units that perform one type of post-processing may be included or post-processing units that perform a plurality of types of post-processing may be included.

Generally, although an image forming apparatus is connected to the former stage side of the post-processing apparatus, it is not necessary for an image forming apparatus to be connected to the former stage of the post-processing apparatus, but a different type of a post-processing apparatus that has a post-processing unit other than the post-processing unit or any other apparatus may be connected thereto.

FIG. 1 is a cross-sectional view that illustrates the mechanical structure of an image forming system.

First, the image forming apparatus 1 will be described.

In the image forming apparatus 1, reference numeral 7 is a sheet feeding unit, reference numeral 8 is a document reading unit, and reference numeral 10 is an image forming unit.

The document reading unit 8 reads an image of a document that is conveyed by an automatic document feeding device (not illustrated in the figure) or a document that is arranged on a platen and temporarily records the image in an image memory, which is not illustrated in the figure, or the like.

The image forming unit 10 includes photosensitive bodies 11C, 11M, 11Y, and 11K that are prepared for colors (cyan, magenta, yellow, black, and the like), and, across peripheral line portions of the photosensitive bodies 11C, 11M, 11Y, and 11K, chargers 12C, 12M, 12Y, and 12K, writing units 13C, 13M, 13Y, and 13K, and developing units 14C, 14M, 14Y, and 14K are arranged. Accordingly, the surfaces of the photosensitive bodies 11C, 11M, 11Y, and 11K that are charged by the chargers 12C, 12M, 12Y, and 12K are exposed for images by the writing units 13C, 13M, 13Y, and 13K based on image information of the document that is recorded in the image memory or the like, and latent images are formed on the surfaces of the photosensitive bodies 11C, 11M, 11Y, and 11K. The latent images are developed by the developing units 14C, 14M, 14Y, and 14K so as to be formed as toner images. The toner images are transferred to an intermediate transfer belt 16 and are transferred from the intermediate transfer belt 16 to a sheet that is conveyed by a sheet feeding unit 20. The sheet to which the toner images have been transferred is heated so as to be fixed by a fixing unit 18, and image forming output (printing) is performed to a sheet ejecting unit 19.

In addition, in the image forming unit 10, cleaning units 15C, 15M, 15Y, and 15K are arranged in correspondence with the photosensitive bodies, which remove remaining toner by being brought into contact with the photosensitive bodies 11C, 11M, 11Y, and 11K on a further rotation direction side than a contact position with the intermediate transfer belt 16 and on a further reverse rotation direction side than the chargers 12C, 12M, 12Y, and 12K. In addition, a cleaning unit 17 that removes remaining toner remaining on the intermediate transfer belt 16 is arranged on a further rotation direction side than a sheet transfer position of the intermediate transfer belt 16 and a further reverse rotation direction side than transfer positions of the photosensitive bodies.

Furthermore, in the image forming apparatus 1, the sheet feeding unit 7 that includes a plurality of sheet feeding trays in which sheets are housed is arranged on the lower side of the image forming unit 10. In addition, a sheet conveying unit 9 is included, which extends from the sheet feeding trays to the image forming unit 10 and from the image forming unit 10 to the sheet ejecting unit 19, and sheets are conveyed through the sheet conveying unit 9 at a predetermined sheet interval.

The photosensitive bodies 11C, 11M, 11Y, and 11K are driven to rotate by a driving motor, which is not illustrated in the figure, and the intermediate transfer belt 16 are driven to rotate with by a driving motor not illustrated in the figure.

The first post-processing apparatus 2 includes a fixing unit 20 as a second fixing unit, as a fixing unit 18 provided in the image forming apparatus 1 is a first fixing unit. The fixing unit 20 performs second fixing by heating and compressing the sheet after receiving the sheet ejected from the sheet ejecting unit 19 of the image forming apparatus 1 in the fixing unit 20. On the sheet ejecting side of the second fixing unit 20, a first conveying path 22 and a second conveying path 23 that are provided a switching unit 21 are included. The first conveying path 22 conveys a sheet ejected from the fixing unit 20 to the sheet ejecting unit 25 so as to be ejected to the second post-processing apparatus 3. The second conveying path 23 conveys a sheet ejected from the fixing unit 20 to the image forming apparatus 1 and passes the sheet to a conveying path 9, thereby enabling to form an image again in the image forming apparatus 1.

The second post-processing apparatus 3 includes a main conveying path 30 that is used for receiving a sheet ejected from the first post-processing apparatus 2 and can convey a sheet to an overlapping conveying unit 32 through a switching unit 31. The main conveying path 30 extends downward through the switching unit 31, and a switching unit 33 is interposed on the lower side thereof. The main conveying path 30 that is disposed immediately behind the switching unit 33 on the lower side also serves as a sheet standby unit. In one switching direction of the switching unit 33, an overlapping path 34 is disposed.

The overlapping conveying unit 32 is configured by a part of the main conveying path, the switching unit 31, the switching unit 33, the overlapping path 34, and the like.

In addition, a stack conveying path 35, which is formed through the switching unit 33, is disposed, and a stack unit 36 is disposed in the conveying direction of the stack conveying path 35.

At the conveyance destination of the main conveying path 30, a post-processing unit 37 is disposed. In this embodiment, as post-processing, flat stitching is performed in the post-processing unit 37. In this figure, the configuration of the post-processing unit 37 is simplified. A sheet ejecting unit 38 is disposed on the downstream side of the post-processing unit 37.

As described above, the post-processing apparatus according to the present embodiment includes the overlapping conveying unit that can overlap sheets and convey the overlapped sheets on the upstream side of the post-processing unit. This overlapping conveying unit can overlap and convey sheets corresponding to different number of overlapping sheets. Here, the structure of the overlapping conveying unit is not particularly limited and may be a structure in which sheets of a predetermined number ejected from an apparatus of the former stage can be overlapped and conveyed in an overlapping manner on the upstream side of the post-processing unit.

The overlapping conveying unit ejects sheets in a state in which the sheets can be received by the post-processing unit and, for example, conveys the sheets to the stack unit.

The overlapping conveying unit is controlled by a control unit. In a case where the time required for the post-processing is equal to or shorter than the sheet interval based on a comparison result of a time comparing unit, the control unit sets an operation of conveying sheets in an overlapping manner by the overlapping conveying unit to be unnecessary. In the present embodiment, it is not excluded to overlap and convey sheets corresponding to a minimum number of overlapping sheets in an overlapping manner even in a case where the time required for the post-processing is equal to or shorter than the sheet interval.

On the other hand, in a case where the time required for the post-processing exceeds the sheet interval, the control unit controls the overlapping conveying unit to overlap and convey sheets in an overlapping manner. In addition, at this time, the number of overlapping sheets may be changed in accordance with the degree of an excess of the time required for the post-processing over the sheet interval. In the control, it is preferable that the number of overlapping sheets is set to a requisite minimum number that does not affect the sheet interval. In the case of the number of overlapping sheets that has not arrived at the requisite minimum, it is difficult to overlap and convey sheets without increasing the sheet interval, whereby the productivity decreases. On the other hand, in a case where overlapping and conveying is performed with the number of sheets that exceeds the requisite minimum number of overlapping sheets, although it does not affect the productivity, the number of overlapping sheets is excessive, whereby a decrease in the conveyance precision, alignment mismatching, or the like may easily occur.

The control unit may be arranged inside the casing of the post-processing apparatus or may be arranged outside the post-processing apparatus, for example, inside the casing of the image forming apparatus or inside the casing of an external device that is connected to a LAN connected to the casing of the post-processing apparatus.

The operation of the overlapping conveying unit 32 will be described with reference to FIG. 2.

A sheet P1 that is received in the main conveying path 30 of the second post-processing apparatus 3 is conveyed along the main conveying path 30 by the switching operation of the switching unit 31 and is conveyed to the overlapping path 34 as the overlapping unit by the switching operation of the switching unit 33 (FIG. 2( a)). When the rear end of the sheet P1 passes through the switching unit 33, the sheet P1 that has been sent to the overlapping path 34 in accordance with the reverse rotation of conveying rollers is switched back and stands by at the main conveying path 30 that is located on the downstream side of the switching unit 33 (FIG. 2( b)). Thereafter, when the next sheet P2 is received from the former stage, while the previous sheet P1 stands by at the main conveying path 30 on the downstream side of the switching unit 33, the sheet P2 is conveyed to the main conveying path 30 on the upstream side and passes through the switching unit 31, and the front end of the sheet P2 is stopped immediately before the switching unit 33. The sheets P2 and P1 are sent to the overlapping path 34 in a same period so as to overlap each other (FIG. 2( d)), and, when the rear end passes through the switching unit 33, both sheets P1 and P2 are switched back together and stand by in an overlapping state at the main conveying path 30 on the downstream side of the switching unit 33 (FIG. 2( e)).

When the post-processing unit 37 can receive sheets, the sheets P1 and P2 are conveyed in the overlapping state to the stack unit 36 that is included in the post-processing unit 37 through the stack conveying path 35 (FIG. 2( f)).

When the number of sheets conveyed to the stack unit 36 arrives at a predetermined number of sheets of a bundle, the sheets are conveyed to the post-processing unit 37, and predetermined post-processing is performed for the sheets.

In the description presented above, although an example has been described in which two sheets are overlapped and conveyed in an overlapping manner, by repeating the above-described sequence, overlapping and conveying of three or more sheets can be performed.

In addition, generally, there is a limit of the number of sheets in the overlapping conveying unit 32, which can be overlapped and conveyed in an overlapping manner, due to a structural reason, and conveyance can be performed by changing the number of overlapping sheets within this limit. Furthermore, an embodiment of the invention is not limited to a specific number of overlapping sheets.

The sheets overlapping each other stand by in the overlapping conveying unit until the sheets can be received by the post-processing unit as described above, and, after the sheets can be received by the post-processing unit, the sheets are ejected from the overlapping conveying unit. It can be determined whether or not sheets can be received based on whether or not the post-processing of the previous bundle of sheets or the like has been completed. In addition, it can be determined whether or not sheets can be received also based on whether or not a predetermined time elapses after the final sheet is sent to the post-processing unit for the post-processing. The time until the post-processing is completed after the final sheet is sent can be determined, and, after a predetermined time required for not interfering with the previous bundle elapses, the sheets may be ejected without any problem even when the post-processing is not completed.

Next, control blocks of the image forming system will be described.

The image forming apparatus 1 includes an image forming apparatus control unit 100 that controls the overall operation of the image forming apparatus 1, and a sheet feeding unit 7, a sheet conveying unit 9, an image forming unit 10, and an image processing unit 113 are connected to the image forming apparatus control unit 100 in a controllable manner. The image forming apparatus control unit 100 acquires the sheet interval that is a conveyance interval of sheets based on the operating conditions of the image forming apparatus 1. The image processing unit 113 performs image processing such as analog processing, A/D conversion, shading correction, and image compressing process for image data that is acquired by a scanner, which is not illustrated in the figure, or the like based on an instruction transmitted from the image forming apparatus control unit 100.

In the sheet feeding unit 7, a sheet is fed from a predetermined sheet feeding tray under the control of the image forming apparatus control unit 100, and conveyance of the sheet from the image forming unit 10 to the sheet ejecting unit 19 is performed by the sheet conveying unit 9 that is controlled by the image forming apparatus control unit 100. In the image forming unit 10, image processing and the like are performed by the image processing unit 113, and an image is written in each color based on the image data that is temporarily stored in a storage unit or the like, thereby performing formation of the image, transfer of the image to the sheet, and the like.

In addition, a sheet feed switching unit 101 is connected to the image forming apparatus control unit 100 in a controllable manner. The sheet feed switching unit 101 performs switching between sheet feeding trays from which a sheet is fed, and, for example, serves its function at a time when automatic switching between sheet feeding trays is performed due to being out of paper in a sheet feeding tray that currently feeds a sheet, a time when switching between sheet feeding trays is performed at a switching period set in advance, or the like. There is a case where the sheet interval changes when switching between sheet feeding trays is performed, and the image forming apparatus control unit 100 acquires a change in the sheet interval that is accompanied with sheet feed switching as information.

Furthermore, a heating unit 110, a temperature detecting unit 111 and a warm-up completion time calculating unit 112 are connected to the image forming apparatus control unit 100 in a controllable manner. The heating unit 110 and the temperature detecting unit 111 are provided in the fixing unit 18, and the fixing unit 18 is heated up to a predetermined temperature by the heating unit 110. The temperature at that time is detected by the temperature detecting unit 111, and the image forming apparatus control unit 100 that receives a detection result of the temperature detecting unit 111 performs heat control through the heating unit 110. In addition, a warm-up completion time that is a time until fixing unit 18 can be operated through heating performed by the heating unit 110 is calculated by the warm-up completion time calculating unit 112. The warm-up completion time calculating unit 112 can calculate the warm-up completion time based on the detection temperature detected by the temperature detecting unit 111, a trend of the change in detection temperature, or the like.

In addition, a serial communication unit 115 is connected to the image forming apparatus control unit 100 in a controllable manner. The serial communication unit 115 is configured to be communicable with the first post-processing apparatus of the later stage.

Furthermore, a time comparing unit 102 is connected to the image forming apparatus control unit 100. The time comparing unit 102 compares the sheet interval and a time required for post-processing performed by the second post-processing apparatus 3. The image forming apparatus control unit 100 is notified of the comparison result. The information of the sheet interval is acquired by the image forming apparatus control unit 100 based on the operation of the image forming apparatus 1 and is also acquired based on a detection result acquired by the second post-processing apparatus 3 to be described later. As an embodiment of the invention, the number of overlapping sheets may be determined by using the information of the sheet interval of only one side.

The image forming apparatus control unit 100 receives the comparison result, compares the time required for post-processing and the sheet interval with each other, and determines the overlapping conveyance performed in the second post-processing apparatus 3. In a case where the time required for post-processing is equal to or shorter than the sheet interval, the overlapping conveyance to be performed in the second post-processing apparatus 3 is determined to be unnecessary. On the other hand, in a case where the time required for post-processing exceeds the sheet interval, the overlapping conveyance is determined to be necessary, and a requisite minimum number of overlapping sheets that is required for the overlapping conveyance is determined in accordance with the degree of an excess of the time required for the post-processing over the sheet interval under a condition that the post-processing can be performed without affecting the sheet interval.

The second post-processing apparatus 3 is notified of the determination result of the overlapping conveyance, which is acquired by the image forming apparatus control unit 100, through the serial communication unit 115 and further through the first post-processing apparatus 2.

The determination of the number of overlapping sheets may be performed at a time when the sheet interval changes, for every time when a sheet is conveyed, for every time when sheets of a predetermined number are conveyed, or the like.

For example, in a case where there is an unexpected factor in the image forming apparatus 1 or there is a factor causing the sheet interval to change in the later stage side of the image forming apparatus 1, for example, in the first post-processing apparatus 2 after the number of overlapping sheets is determined based on the sheet interval that is derived based on the operating conditions of the image forming apparatus 1, by changing the number of overlapping sheets based on the sheet interval that is detected by the second post-processing apparatus 3 or the like, the number of overlapping sheets that is appropriate to the situation can be determined.

The first post-processing apparatus 2 includes a first post-processing apparatus control unit 200 that controls the overall operation of the first post-processing apparatus 2, and an upper-stage serial communication unit 201 is connected to the first post-processing apparatus control unit 200 in a controllable manner. The upper-stage serial communication unit 201 is connected to the serial communication unit 115 of the image forming apparatus 1 so as to be communicable.

In addition, a lower-stage serial communication unit 202 is connected to the first post-processing apparatus control unit 200 in a controllable manner, and the first post-processing apparatus control unit 200 is configured to be communicable with the second post-processing apparatus 3 disposed on the later stage through the lower-stage serial communication unit 202.

Furthermore, a sheet conveying unit 205 is connected to the first post-processing apparatus control unit 200 in a controllable manner. The sheet conveying unit 205 conveys a sheet ejected from the image forming apparatus 1 disposed on the previous stage, conveys the sheet to the image forming apparatus 1 or the second post-processing apparatus 3 disposed on the later stage, and is configured by the switching unit 21, the first conveying path 22, and the second conveying path 23 described above.

In addition, a heating unit 210, a temperature detecting unit 211, and a warm-up completion time calculating unit 212 are connected to the first post-processing apparatus control unit 200 in a controllable manner. The heating unit 210 and the temperature detecting unit 211 are provided in the fixing unit 20, and the fixing unit 20 is heated up to a predetermined temperature by the heating unit 210. The temperature at that time is detected by the temperature detecting unit 211, and the first post-processing apparatus control unit 200 that receives a detection result of the temperature detecting unit 211 performs heat control through the heating unit 210. In addition, a warm-up completion time that is a time until fixing unit 20 can be operated through heating performed by the heating unit 210 is calculated by the warm-up completion time calculating unit 212. The warm-up completion time calculating unit 212 can calculate the warm-up completion time based on the detection temperature detected by the temperature detecting unit 211, a trend of the change in detection temperature, or the like.

The second post-processing apparatus 3 includes a second post-processing apparatus control unit 300 that controls the overall operation of the second post-processing apparatus 3, and an upper-stage serial communication unit 301 is connected to the second post-processing apparatus control unit 300 in a controllable manner. The upper-stage serial communication unit 301 is connected to the lower-stage serial communication unit 202 of the first post-processing apparatus 2 so as to be communicable therewith. As a result, the second post-processing apparatus 3 can communicate with the first post-processing apparatus 2 and can communicate with the image forming apparatus 1 through the first post-processing apparatus 2.

A sheet conveying unit 302, an overlapping conveying unit 32, and a sheet detecting unit 303 are connected to the second post-processing apparatus control unit 300 in a controllable manner. The sheet conveying unit 302 conveys a sheet ejected from the first post-processing apparatus 2 of the former stage within the second post-processing apparatus 3 and includes a main conveying path 30, a switching unit 31, a switching unit 33, an overlapping path 34, a stack conveying path 35, and the like.

In addition, the overlapping conveying unit 32 is configured by a part of the main conveying path 30, the switching unit 33, the overlapping path 34, the stack conveying path 35, and the like. In the second post-processing apparatus control unit 300, overlapping and conveying of sheets is performed in accordance with the number of overlapping sheets that is determined by comparing the time required for post-processing performed by the post-processing unit 37 with the sheet interval. In a case where the overlapping conveyance is unnecessary, the overlapping conveyance is not performed.

Accordingly, the second post-processing apparatus control unit 300 corresponds to a control unit according to an embodiment of the invention.

The sheet detecting unit 303 is arranged in the main conveying path 30, detects a sheet that is conveyed, and the detection result is used for controlling the switching units 31 and 33, the conveyance of the sheet, and the like. In addition, the second post-processing apparatus control unit 300 can acquire a sheet interval between sheets that are conveyed within the second post-processing apparatus 3 based on the sheet detecting result acquired by the sheet detecting unit 303. The information of the sheet interval that is acquired by the second post-processing apparatus control unit 300 is transmitted to the image forming apparatus 1.

The post-processing unit 37 is connected to the second post-processing apparatus control unit 300 in a controllable manner. In the post-processing unit 37, flat stitching is performed.

In addition, a post-processing time calculating unit 310 is connected to the second post-processing apparatus control unit 300. The post-processing time calculating unit 310 calculates a processing time that is required for the post-processing unit 37. In the calculation process, a calculation is performed in consideration of the number of sheets, the type of the sheets to be stitched in a flat manner, and the like. The calculation result acquired by the post-processing time calculating unit 310 is transmitted to the second post-processing apparatus control unit 300. The image forming apparatus 1 is notified of the calculation result through the upper-stage serial communication unit 301 and the first post-processing apparatus 2 by the second post-processing apparatus control unit 300. The calculation result is received by the serial communication unit 115 and is transmitted to the image forming apparatus control unit 100. The image forming apparatus control unit 100 transmits the calculation result to the time comparing unit 102 so as to be provided for the comparison of the time required for the post-processing and the sheet interval.

Since the time that is required for post-processing differs depending on factors such as the number of sheets forming a bundle in the post-processing, the content of the post-processing, the type of sheets, and the processing capability of the post-processing apparatus, generally, such factors are prepared as parameters in advance, so that the time required for the post-processing can be calculated by the post-processing time calculating unit. The post-processing time calculating unit can be configured by a CPU, a program that operates the CPU, a storage unit in which the parameters and the like are stored, and the like. Among the above-described factors, the number of sheets, the content of the post-processing, the type of sheets, and the like are acquired as information by the image forming apparatus, and the information can be used for the above-described calculation process. In addition, information according to the configuration of the post-processing apparatus such as the processing capability of the post-processing apparatus may be maintained by the post-processing apparatus or may be acquired in advance by the image forming apparatus to which the post-processing apparatus is connected.

The post-processing time calculating unit may be arranged inside the casing of the post-processing apparatus or may be arranged outside the post-processing apparatus, for example, inside the casing of the image forming apparatus or inside the casing of an external device that is connected to a LAN connected to the casing of the post-processing apparatus.

The sheet interval of sheets ejected from the former stage is acquired as information on the former stage side, and the information can be used. Alternatively, the information relating to the sheet interval may be acquired by arranging a sensor that detects a sheet interval in the former stage side or in the post-processing apparatus, or the like. In addition, both the sheet interval acquired as the information by the former stage side and the detection result acquired by the sensor may be used together. In such a case, even in a case where the sheet interval become particularly larger than that of a general case, the number of overlapping sheets can be appropriately changed based on the detection result regardless of the information of the sheet interval that is acquired on the former stage side.

The sheet interval also is changed by performing image adjustment in the image forming unit that is arranged in the image forming apparatus, changing a sheet feeding tray (sheet feeding stage) of sheets to which images are transformed, or changing the type of sheets.

Accordingly, the information of the sheet interval that is acquired on the image forming apparatus side is also changed in accordance with the changes in the situation.

The time required for post-processing that is calculated by the post-processing time calculating unit and the sheet interval are compared with each other by the time comparing unit. Here, it is determined whether the time required for the post-processing is longer than the sheet interval or the time required for the post-processing is equal to or shorter than the sheet interval. The time comparing unit may be arranged inside the casing of the post-processing apparatus or may be arranged outside the post-processing apparatus, for example, inside the casing of the image forming apparatus or inside the casing of an external device that is connected to a LAN connected to the casing of the post-processing apparatus.

In addition, a post-processing unit entrance availability determining unit 311 is connected to the second post-processing apparatus control unit 300. The post-processing unit entrance availability determining unit 311 determines whether or not post-processing has been completed and a sheet can be entered. In addition, even in a case where the post-processing has not been completed, it is determined whether a final page of a bundle for which the post-processing is performed has passed based on the detection result acquired by the sheet detecting unit 303. In this determination process, an elapsed time after the passage of the sheet is measured, and it is determined whether or not the elapsed time has passed a predetermined time. The predetermined time is a time in which the final page is stacked in the stack unit 36 and is conveyed to the post-processing unit 37 side, and a next sheet can be received by the stack unit 36, and, as it reaches the time, the next sheet can be conveyed to the stack unit 36 without being interfered with the sheets of the previous bundle. Even in such a case, it is determined that the entrance to the post-processing unit can be performed.

Next, a state in which overlapping and conveying is controlled to be performed by the second post-processing apparatus 3 will be described with referring to FIG. 4.

FIG. 4( a) illustrates a state in which a time required for post-processing is as expected, and the post-processing can be performed without affecting the sheet interval by performing overlapping and conveying with a predetermined number of overlapping sheets (for example, four sheets).

However, in a case where the sheet interval becomes larger due to a factor of the main body of the image forming apparatus 1, it is necessary to perform overlapping and conveying, and the overlapping and conveying is performed with a predetermined number of overlapping sheets (FIG. 4( b)). However, even when a state is formed in which the sheet interval becomes sufficiently larger, and the overlapping conveyance is unnecessary, the overlapping and the conveying with the predetermined number of sheets are performed. This example corresponds to a conventional overlapping conveyance operation.

On the other hand, according to an embodiment of the invention, when overlapping and conveying is determined to be unnecessary based on the state of the sheet interval, the overlapping and conveying is not performed any more, and the number of overlapping sheets can be set to a requisite minimum number. In FIG. 4( c), since the sheet interval becomes sufficient during the overlapping and conveying operation, the overlapping and conveying operation is stopped at a time point when the sheet interval is secured, and the number of overlapping sheets is limited to two, whereby the number of overlapping sheets can be minimized.

According to the present embodiment, the number of overlapping sheets in the overlapping conveying unit can be changed in accordance with the relation between the time required for the post-processing and the sheet interval, and, in a case where the time required for the post-processing is longer than the sheet interval, a minimum requisite number of overlapping sheets is set, and the number of sheets can be decreased. Accordingly, the overlapping and conveying can be performed without determining the number of overlapping sheets in advance. On the other hand, in a case where the time required for the post-processing is equal to or shorter than the sheet interval, the post-processing can be performed without overlapping sheets in the overlapping conveying unit.

Another example will be described with reference to FIG. 5.

In this example, a case is considered in which the sheet interval becomes larger due to a factor of the first post-processing apparatus.

FIG. 5( a) illustrates a state in which a time required for post-processing is as expected, and the post-processing can be performed without affecting a sheet interval. The overlapping and conveying state is not illustrated.

FIG. 5( b) illustrates a state in which a sheet interval becomes larger due to a factor of the first post-processing apparatus.

In FIG. 5( c), the number of sheets that are overlapped and conveyed in an overlapping manner is changed in accordance with a sheet interval, a requisite minimum sheet interval is secured, and the overlapping and conveying is stopped so as to minimize the number of overlapping sheets.

Next, the sequence of a control process in which the number of overlapping sheets in the overlapping conveying unit is changed in accordance with the sheet interval between sheets will be described with reference to flowcharts illustrated in FIG. 6. The sequence of the control process is performed by the second post-processing apparatus control unit 300.

In the sequence illustrated in FIG. 6( a), a sheet ejected from the first post-processing apparatus 2 is introduced into the second post-processing apparatus 3 so as to start conveyance in Step s1, and the conveyance is detected by the sheet detecting unit 303 in the main conveying path 30 in Step s2. The process waits until detection of the conveyance is made (No in Step s2), and when the detection of conveyance is made (Yes in Step s2), it is determined whether or not a previous bundle is in the middle of the post-processing in Step s3. In a case where the previous bundle is not in the middle of the post-processing (No in Step s3), the conveyed sheet is ejected to the post-processing unit in Step s4. On the other hand, in a case where the previous bundle is in the middle of the post-processing (Yes in Step s3), the sheet is conveyed to the overlapping conveying unit 32 in Step s5. When the conveyance of the sheet to the overlapping conveying unit 32 is performed, sheets are conveyed to the overlapping conveying unit with the number of overlapping sheets that is determined based on a comparison of the time required for the post-processing and the sheet interval. In addition, in this embodiment, although the comparison of the time required for the post-processing and the sheet interval and the determination of the number of overlapping sheets are performed by the image forming apparatus, the comparison and the determination may be performed by the second post-processing apparatus 3. Furthermore, in a case where a sheet may not be ejected to the post-processing unit, and the number of overlapping sheets in the overlapping unit arrives at an upper limit so as to cause a problem, it is necessary to increase the sheet interval.

The time that is required for the post-processing can be acquired through the sequence illustrated in FIG. 6( c).

The sheet information is acquired from the image forming apparatus 1 in Step s20, and the post-processing information is further acquired in Step s21. In the second post-processing apparatus 3, information that is necessary for the post-processing can be calculated based on the above-described information by the post-processing time calculating unit 310.

The sequence of a control process in which sheets are ejected to the post-processing unit in a state that sheets are overlapped with each other in the overlapping conveying unit will be described with reference to the flowchart illustrated in FIG. 6( b).

It is checked whether or not a sheet can be received by the post-processing unit 37 in Step s10.

The process waits with the check of the result until a next sheet can be received by the post-processing unit 37 (No in Step s11, then return to Step s10). When the next sheets can be received by the post-processing unit 37 (Yes in Step s11), the next sheets are ejected to the post-processing unit 37 in Step s12.

Next, a detailed sequence of Step s10 in which it is checked whether or not a sheet can be received by the post-processing unit 37 will be described with reference to the flowchart illustrated in FIG. 6( d).

First, it is determined whether or not a state is formed in which sheets can enter into the post-processing unit 37 in Step s30. When the post-processing is completed by the post-processing unit 37, sheets can be entered into the post-processing unit 37 (Yes in Step s30). When sheets can be entered into the post-processing unit 37, it is checked that the sheet can be ejected to the post-processing unit, and the process ends.

On the other hand, in a case where sheets can not be entered into the post-processing unit 37 (No in Step s30), it is determined whether or not a required time elapses after the passage of the final sheet of the previous bundle in Step s31. This required time is a time in which the next sheets can be entered into the post-processing unit without being interfered with the previous bundle in the post-processing unit even when the next sheets are started to convey to the post-processing unit at that timing. This time is acquired the information in advance by acquiring it when the time required for the post-processing is acquired or the like.

When the required time elapses after the passage of the final page of the previous bundle (Yes in Step s31), it is determined that sheets can be ejected in Step s32. On the other hand, when the required time has not elapsed after the passage of the final page of the previous bundle (No in Step s31), the process ends without determining that sheets can be ejected.

According to the embodiment of the invention, since overlapping sheets of a minimum number can be overlapped and conveyed in an overlapping manner by an overlapping conveying unit, improved alignment of sheets can be secured. In addition, a time in which the overlapping state is maintained by the overlapping conveying unit can be shortened.

Furthermore, in a case where it is desired to convey the minimum overlapping number of sheets, it is not necessary to be aware of a post-processing apparatus that is connected to the upstream side.

As above, while the above-described embodiment of the invention has been presented, the invention is not limited to the content of the above-described embodiment, and an appropriate change can be made therein in the range not departing from the scope of the invention. 

1. A post-processing apparatus comprising: a post-processing unit to perform post-processing for a sheet ejected from a former-stage apparatus; a post-processing time calculating unit to calculate a time required for the post-processing based on a content of the post-processing; a time comparing unit to compare the time required for the post-processing and a sheet interval between sheets ejected from the former-stage apparatus with each other; an overlapping conveying unit to overlap a plurality of sheets ejected from the former-stage apparatus and convey the overlapping sheets on an upstream side of the post-processing unit; and a control unit to control the overlapping conveying unit, wherein the control unit changes the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of sheets ejected from the former-stage apparatus in a case where the time required for the post-processing is determined to exceed the sheet interval based on a comparison result of the time comparing unit.
 2. The post-processing apparatus according to claim 1, wherein the control unit changes the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of the sheets ejected from the former-stage apparatus at the time of maintaining same set in the plurality sets for printing in an image forming apparatus arranged on a former stage of the post-processing apparatus.
 3. The post-processing apparatus according to claim 1, wherein the control unit changes the number of overlapping sheets in the overlapping conveying unit in accordance with the sheet interval of the sheets ejected from the former-stage apparatus at the time of occurring different set in the plurality sets for printing in an image forming apparatus arranged on a former stage of the post-processing apparatus.
 4. The post-processing apparatus according to claim 1, wherein the control unit performs control of ejecting the sheets overlapped each other in the overlapping conveying unit toward the post-processing unit in a case where the post-processing unit disposed on a downstream side of the overlapping conveying unit is in a state in which sheets can be received.
 5. The post-processing apparatus according to claim 4, wherein the control unit determines the state in which sheets can be received based on whether or not the post-processing for sheets sent to the post-processing unit in advance has been completed.
 6. The post-processing apparatus according to claim 4, wherein the control unit determines the state in which sheets can be received based on whether or not a predetermined time has elapsed after a final sheet is sent to the post-processing unit for the post-processing.
 7. The post-processing apparatus according to claim 1, wherein the former-stage apparatus is an image forming apparatus.
 8. The post-processing apparatus according to claim 1, wherein the former-stage apparatus includes a different type of a post-processing apparatus that has a post-processing unit other than the post-processing unit.
 9. An image forming system comprising: an image forming apparatus to form an image and transfer the image to the sheet; a post-processing apparatus being located on a later stage side of the image forming apparatus and including a post-processing unit to perform post-processing for a sheet ejected from a former-stage apparatus and an overlapping conveying unit to overlap a plurality of sheets ejected from the former-stage apparatus and convey the overlapping sheets on an upstream side of the post-processing unit; a post-processing time calculating unit to calculate a time required for the post-processing based on a content of the post-processing; a time comparing unit to compare the time required for the post-processing and a sheet interval between sheets ejected from the former-stage apparatus of the post-processing apparatus with each other; and the control unit according to claim
 1. 10. The image forming system according to claim 9, wherein at least one of a different type of a post-processing apparatus having a post-processing unit other than the post-processing unit is connected in sequence to the former stage of the post-processing apparatus in a later stage side of the image forming apparatus. 